Traditionally, voice calls are transported entirely over the end-to-end, circuit-based Public Switched Telephone Network (PSTN). However, considerable attention has been directed toward the implementation of real-time communication across computer data networks, and particularly the ability to route voice traffic over these networks. Interest has also been raised in using Voice over IP (VoIP) solutions to facilitate voice communication between originating and terminating PSTN end points and enterprise or private network end points served by PSTN Switches, Private Branch Exchanges (PBX), or IP end points in Local Area Networks (LAN) via the Internet or private IP network. Using a private IP network or Internet for long haul routing substantially bypasses the PSTN. When bypassing a PSTN, pulse code modulated (PCM) voice traffic is processed into IP (or ATM) packets, transported over the private IP network or Internet (or ATM network), and then processed back to PCM voice. To facilitate such call routing, originating and terminating End Office (EO) switches are connected to PSTN/IP (or PSTN/ATM) gateways that reside as hosts on the IP (or ATM) network.
Unfortunately, when a new VoIP telephone voice call is established (with the intent of it being routed over the IP network), there are no means to evaluate the level of congestion of the core IP network. In other words, it is possible to have too many new voice calls being introduced to the network at the same time so that the core IP network is overloaded. Under such a condition, it is highly likely that packets of information that contain the voice data will either be dropped, or delayed from arriving at the destination. These conditions result in poor Quality of Service (QoS) of the network.
The problem of QoS is further compounded when the communication network must handle voice calls of different priority levels or classifications, which exist, for example, in a Defense Switched Network (DSN). That is, there is a need to provide a differentiation in quality based on the priority level of the call as well as provide quality to all calls in the system. The highest priority calls, for instance, must not be blocked, and must receive the best voice quality, even during traffic overloads and IP network congestion. These types of conditions can arise during crisis or partial network failures. For example, existing architectures tend to drop established calls (i.e., calls of lower precedence) to increase network resources for use by higher priority calls. This process is disruptive and not user-friendly.